By way of background, light collimating screens are used in many optical applications. These devices typically control the direction of light passing through the screen.
Light control films, or light collimating screens, have various applications such as contrast enhancement and improved sunlight readability for displays. Light collimating screens are also useful for ensuring confidential viewing on computer monitors so that unauthorized observers will have the line of sight blocked. Such films are also used to direct light to where it is needed and away from where it is not, e.g., to hide the light source in incandescent lighting.
Other industrial applications of light collimating screens are implemented where the direction of light is advantageously controlled, such as is in connection with optical sensing applications. In this regard, for example, light collimators are currently used as part of the paper mover in an image rendering device such as a printer. However, these screens restrict the viewing angle only in one direction. In order to achieve collimation in all in-plane directions, two screens would have to be laid on top of and oriented perpendicular to each other.
Along these lines, commercially available light control films or screens generally comprise a plastic layer(s) containing closely spaced microlouvers. With reference to FIG. 1, a portion 10 of a light collimating screen is shown. The microlouvers, such as that shown at 12, are typically black in color and formed as equidistant polymeric walls. These walls are embedded in a transparent polymer material 14. The louvers, such as that shown at 12, simulate a tiny Venetian blind blocking out unwanted ambient light and controlling the direction of light. Typical films are about 330 microns thick. The black micro-louvers, such as that shown at 12, are about 20 microns wide and the regions filled with polymeric material 14 are about 80 microns wide. This results in a fill factor of 80% for the light channeling regions. The measured maximum viewing angle, as defined and illustrated in FIG. 1, is approximately 50 degrees. It should be noted that the walls are formed in these devices at angles of 0 degrees, as shown, or at other tilted angles, depending upon the application.
FIG. 2 illustrates an application of the conventional light collimating screen identified above. A portion 20 of a light collimating screen and an underlying display shows that the walls 22 are generally equidistant and spaced using a transparent polymeric material 24.
As should be apparent from FIGS. 1 and 2, the conventional light collimating screens collimate the light in only a single direction. As noted above, to achieve collimation in other directions, two screens would have to be layered and oriented perpendicular to each other.
For many applications, it would be advantageous to collimate light through a light collimating screen in more than a single direction.